The invention relates to investment casting. More particularly, the invention relates to the removal of metallic casting cores from cast parts.
Investment casting is commonly used in the aerospace industry. Various examples involve the casting of gas turbine engine parts. Exemplary parts include various blades, vanes, seals, and combustor panels. Many such parts are cast with cooling passageways. The passageways may be formed using sacrificial casting cores.
Exemplary cores include ceramic cores, refractory metal cores (RMCs), and combinations thereof. In exemplary combinations, the ceramic cores may form feed passageways whereas the RMCs may form cooling passageways extending from the feed passageways through walls of the associated part.
After the casting of the part (e.g., from a nickel- or cobalt-based superalloy), the casting shell and core(s) are destructively removed. Exemplary shell removal is principally mechanical. Exemplary core removal is principally chemical. For example, the cores may be removed by chemical leaching. Exemplary leaching involves use of an alkaline solution in an autoclave. Exemplary leaching techniques are disclosed in U.S. Pat. Nos. 4,141,781, 6,241,000, and 6,739,380.
Especially where long and/or fine passageways are concerned, the leaching may be quite time-consuming. Problems faced in leaching include: minimizing adverse effects on the cast part; effective leaching of both metallic and ceramic cores where a combination is used; residual contaminants from the leaching media; potential exposure to hazardous materials; safe/environmentally-friendly disposal of residual leaching media and leachant by-products.